US2227929A - Pantograph antenna - Google Patents

Description

Patente-d Jan. 7, 1941 UNITED STATES PATE-NT i oer-TCE j y2,227,929 ArAN'rVOGRAPH ANTENNA De Witt Rugg Goddard, Riverhead, N. Y., assigner to Radio Corporation of America, a corporation of Delaware Application June 29, 1939, Serial No. 281,915

5 claims. (o1. 25o-11) This invention relates to a directional antenna system which is particularly adapted to measure the vertical arrival angle of short Wave radiations.

In the past the measurement of the vertical angle of arrival of radio signals has been accomplished with considerable difjculty and has necessitated the use of complicated receiving equipment. In addition, the actual angle of arrival was obtained only after considerable computations had been, made. It is therefore an object of this invention to provide a directive antenna system by means of which the vertical angle of arrival of radiated waves may be measured directly. Further objects of this invention include the provision of an improved directional antenna system; the provision of a readily adjustable directional antenna; the provision of a directional antenna whichy is not adversely affected by waves which are reflected from the surface of the earth; and the provision of a directional antenna system which may be used to provide an inclined plane of zero signal which may be used to guide aircrafts to blind landings.

This invention will be better understood from the following description` when considered in connection with the accompanying drawing, in which Figure 1 illustrates the electrical connections of an antenna systemin accordance with this invention; Figure 2'is a plan view of a mechanical arrangement suitable for adjusting the angle of reception of the directive antenna system; and Figure 3 is a4 perspective View illustrating the general arrangement and connection .of the antennas used in the directive system herein proposed.

Referring to the drawing, the antenna system comprises four mutually parallel dipole antennas A, B, C and D which are supported at the four corners of a parallelogram, the sides of which are substantially a half wave length long at the operating frequency, the diagonals of which lie, respectively, in vertical and horizontal planes.

Referring particularly to Figures 1 and 3, dipole antennas A and B are connected by a transmission line L that contains one reversal, that is, the right hand portion of dipole A is connected to the left hand portion of dipole B, and vice versa. Dipoles C and D are connected in the same fashion, and dipoles C and B are likewise similarly connected. At any convenient point, adjacent dipole B, for example, a transmission line T is connected between the antenna system and a receiver R. v

The arrangement shown produces a null or point of zero reception for signals arriving at the angle a. line through antennas A and'B makes'to the ground. The voltage at antenna B whichis' produced by a signal Whose Wave iront is proceed;4 ing in the direction of the arrows P parallel to a line drawn through antennas A and B is Zero, as will now beexplained. The voltageat antenna B is the resultant of the voltage picked up by all the antennas. That produced by antenna A is in phase opposition to that produced' by'antennaB due to the reversal of the connection in transmis sionline L. Likewise, the voltage produced by antenna C is in phase opposition to the voltage produced by antenna. D due to the reversal of. 1*'5 transmission line M. Consequently, there is noy voltage present at antennas B or D, and the transmission line N connecting the latter vantennas transfers no energy and the lreceiverflt receives no signals.

Consideration will now be given tothe effect of the energy which is reflected vfrom the ground and which impinges on the dipole antennas. The reflected energy will have the same angle to the ground as the directly received energy but :the Wave front will proceed in a direction indicated by the arrows O, since the angle of incidence is equal to the angle of reflection. The reflected energy travels in a direction which is parallel to a line passing through antennas C and A, which is also parallel to a line passing through antenna B and D. The reflected energy will therefore induce a voltage in antenna C which will travel through transmission lines M, N and L and will arrive at antenna A at a time which is equal to three half wave lengths later. also suffer three phase reversals while traversing this path. Each half wave length of transmission lineand each phase reversal', respectively, provide phase shift, so that the total phase shift experienced by the induced voltage in the three sections is equal to 1080", or three complete revolutions. In other words, the voltage that appears at dipole antenna A due to the voltage induced in antenna C is in phase with the voltage at antenna C. However, the voltage picked up by dipole A is in phase opposition to that picked up by dipole C due to the half Wave spacing between C and A. Therefore, the voltage at A is bucked oui-l by the voltage induced in antenna C. This combination of voltages is, of course, true for any point on the transmission lines N, M or L, and is therefore true at the point at which transmission line T is connected to the system. The receiver R, therefore, receives no signal from voltages which are induced in antennas A and C. An-

This voltage will,

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tennas B and D are likewise in line with the reected signal wave front, are likewise spaced a half wave length apart, and the induced voltages are likevn'se in phase opposition so that no signal will be reproduced in the receiver due to voltages induced in antennas B and D. It is apparent, therefore, that the antenna arrangement illustrated is notI receptive to signals arriving from the directions indicated by the arrows O and P. Signals arriving from directions other than 0 and P, however, are not completely balanced out since the eiective distance between the various dipole antennas is not equal to a half wave length at any other angle of approach.

In order to provide a directive antenna system which is readily adapted to be used for the measurement of signals arriving at an unknown angle, an arrangement similar to that illustrated in Fig. 2 is proposed. Each of the four dipole antennas is held at a xed distance from each adjacent antenna by any suitable insulating means the length of which is preferably adjustable. For example, the transmission lines themselves may be rigid telescopic conductors. The lengths of the dipole antennas are also preferably adjustable to permit operation over a range of frequencies. The lower dipole C is held in fixed position, while the upper dipole A is arranged to be moved vertically in a rigid insulated support S so that the angle of reception may be adjusted. The arrangement is similar to a pantograph, the insulating spacers having exible couplings at the respective antennas. By moving antenna A in a vertical direction the angle of minimum reception is varied, and the actual angle may be determined by means of a Calibraw tion which is provided along the vertical supporting member S. The angle of approach is therefore directly indicated, and computations are not necessary. In Figure 2, the antenna is illustrated in two positions. When extended; antennas A', B', and D produce a null at the receiver for a signal which arrives at an angle U while in its lower position the antenna produces a null indication for signals arriving at an angle V.

While I have illustrated this antenna in connection with a receiver it is also adapted to be (used in connection with a transmitter. In such `an application it will provide a radiation pattern which has a plane of zero signal which makes an angle with the ground. This angle is readily adjustable as will be seen, and may be used to direct the flight of an aircraft, for example, to permit blind landings.

I claim:

1. A directional antenna system comprising four mutually parallel horizontal dipole antennas having oppositely extending arms, said antennas being positioned so as to define the corners of a parallelogram the diagonals of which are, respectively, horizontal and vertical, and conducting means connected between said oppositely extending arms so that currents induced in said conducting means by one of said antennas are in phase opposition to currents induced in said conducting means by another of said antennas.

2. A directional antenna system comprising a plurality of mutually parallel dipole antennas 'having oppositely extending arms, means for supporting said dipole antennas at the four corners of a parallelogram the diagonals of which are, respectively, horizontal and vertical, a pair of conductors for connecting alternate arms of said antennas in parallel so that currents induced in said conductors by one of said antennas are in phase. opposition to currents simultaneously induced in an adjacent antenna, and means for varying the relative positions of said dipole antennas to change the vertical angle of minimum response.

3. A directional antenna system comprising a plurality of mutually parallel dipole antennas, means for supporting said antennas at the four corners of a parallelogram, the sides of which are substantially a half wave length long at the operating frequency, means connected between adjacent dipole antennas for connecting said dipole antennas in parallel, the polarity of said connecting means being reversed between adjacent antennas, and means for varying the position of one of said antennas with respect to a diagonally positioned antenna to adjust said system to indicate the horizontal angle of approach of radio waves impinging on said system.

4. A directional antenna system comprising a plurality of mutually parallel dipole antennas, means for supporting said antennas at the four corners of a parallelogram., the sides of which are substantially a half wave length long at the operating frequency and the diagonals of which lie respectively in vertical and horizontal planes, means connected between adjacent dipole antennas for connecting said dipole antennas in parallel, the polarity of said connecting means being reversed between adjacent antennas, and means for varying the position of one of said antennas with respect to a diagonally positioned antenna to adjust said system to indicate the horizontal angle of approach of radio waves impinging on said system.

5. A device of the character described in claim 4 which includes indexing means associated with said one antenna for indicating the vertical angle of minimum reception of said system.

DE WITT RUGG GODDARD.

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